@[TOC]

从源码看Thread中定义的六种线程状态

Thread类位于java.lang包下，在Thread类中有一个枚举类型State，State中定义了线程的六种状态。源码如下：

java.lang.Thread.State

public enum State {
        /**
         * Thread state for a thread which has not yet started.
         */
        NEW,

        /**
         * Thread state for a runnable thread.  A thread in the runnable
         * state is executing in the Java virtual machine but it may
         * be waiting for other resources from the operating system
         * such as processor.
         */
        RUNNABLE,

        /**
         * Thread state for a thread blocked waiting for a monitor lock.
         * A thread in the blocked state is waiting for a monitor lock
         * to enter a synchronized block/method or
         * reenter a synchronized block/method after calling
         * {@link Object#wait() Object.wait}.
         */
        BLOCKED,

        /**
         * Thread state for a waiting thread.
         * A thread is in the waiting state due to calling one of the
         * following methods:
         * <ul>
         *   <li>{@link Object#wait() Object.wait} with no timeout</li>
         *   <li>{@link #join() Thread.join} with no timeout</li>
         *   <li>{@link LockSupport#park() LockSupport.park}</li>
         * </ul>
         *
         * <p>A thread in the waiting state is waiting for another thread to
         * perform a particular action.
         *
         * For example, a thread that has called <tt>Object.wait()</tt>
         * on an object is waiting for another thread to call
         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
         * that object. A thread that has called <tt>Thread.join()</tt>
         * is waiting for a specified thread to terminate.
         */
        WAITING,

        /**
         * Thread state for a waiting thread with a specified waiting time.
         * A thread is in the timed waiting state due to calling one of
         * the following methods with a specified positive waiting time:
         * <ul>
         *   <li>{@link #sleep Thread.sleep}</li>
         *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
         *   <li>{@link #join(long) Thread.join} with timeout</li>
         *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
         *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
         * </ul>
         */
        TIMED_WAITING,

        /**
         * Thread state for a terminated thread.
         * The thread has completed execution.
         */
        TERMINATED;
    }

6中线程状态：

• 1、NEW
  尚未启动的线程的线程状态。
• 2、RUNNABLE
  可运行线程的线程状态。
  可运行的线程状态正在Java虚拟机中执行，但它可能等待操作系统的其他资源如处理器。
• 3、BLOCKED
  线程阻塞等待监视器锁定的线程状态。
  处于synchronized同步代码块或方法中被阻塞。
• 4、WAITING
  等待线程的线程状态。
  处于等待状态的线程正在等待另一个线程执行特定的操作。
• 5、TIMED_WAITING
  具有指定等待时间的等待线程的线程状态。
• 6、TERMINATED
  终止线程的线程状态。
  线程正常完成执行或者出现异常。

==注：线程在给定时间点只能处于一种状态。这些状态是虚拟机状态，不反映任何操作系统线程状态。==

调用getState方法可以得到当前线程的状态。

public class ThreadTest {
    public static void main(String[] args) {
        Thread thread1 = new MyThread();

        System.out.println("thread1的线程状态：" + thread1.getState());
        thread1.start();
        System.out.println("thread1的线程状态：" + thread1.getState());

    }
}

class MyThread extends Thread{
    @Override
    public void run() {
        System.out.println(this.getName() + " is running。。。");
    }
}

线程状态的变化

1.线程正常运行结束的状态变化

public class ThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("当前线程正在执行-------");
                System.out.println("线程正在执行时的线程状态：" + Thread.currentThread().getState().toString());
            }
        });
        System.out.println("创建线程后，调用start前的线程状态：" + thread1.getState().toString());
        thread1.start();
        Thread.sleep(2000L); // 等待thread1执行结束，再看状态
        System.out.println("---等待两秒，线程执行结束后的状态：" + thread1.getState().toString());
        //thread1.start(); //当线程终止之后，再进行调用，会抛出IllegalThreadStateException异常
    }
}

程序运行结果显示：

• 当一个线程被创建时（还未调用start方法）处于NEW状态；
• 调用start方法后，线程开始执行，此时线程处于RUNNABLE状态；
• 线程继续执行，一段时间后，线程正常执行结束，此时线程处于TERMINATED状态。
  ==（新建 -> 运行 -> 终止，NEW-> RUNNABLE-> TERMINATED）==

==注意：当线程执行结束之后，再进行调用，会抛出IllegalThreadStateException异常==

2.线程执行过程中等待一段时间再继续执行结束的状态变化

public class ThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("当前线程正在执行-------,需要花费两秒时间------");
                try {   // 将线程2移动到等待状态，2s后自动唤醒
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("线程正在执行时的线程状态：" + Thread.currentThread().getState().toString());
            }
        });
        System.out.println("创建线程后，调用start前的线程状态：" + thread2.getState().toString());
        thread2.start();
        Thread.sleep(200L); // 等待200毫秒，再看状态
        System.out.println("等待200毫秒（线程还没执行结束），线程的状态：" + thread2.getState().toString());
        Thread.sleep(3000L); // 再等待3秒，让thread2执行完毕，再看状态
        System.out.println("等待3秒（线程执行结束），线程的状态：" + thread2.getState().toString());
    }
}

程序运行结果显示：

• 当一个线程被创建时（还未调用start方法）处于NEW状态；
• 调用start方法后，线程开始执行，此时线程处于RUNNABLE状态；
• 当线程运行过程中需要等待一段时间时，线程进入TIMED_WAITING状态
• 线程继续执行，一段时间后，线程正常执行结束，此时线程处于TERMINATED状态。
  ==（新建 -> 运行 -> 等待 -> 运行 -> 终止，NEW-> RUNNABLE->TIMED_WAITING->RUNNABLE-> TERMINATED）==

3.线程执行过程中等待其他线程被阻塞，然后继续执行到结束的状态变化

public class ThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (ThreadState.class) {
                    System.out.println("当前线程正在执行-------");
                    System.out.println("线程正在执行时的线程状态：" + Thread.currentThread().getState().toString());
                }
            }
        });
        synchronized (ThreadState.class) {
            System.out.println("没调用start方法，thread3当前状态：" + thread3.getState().toString());
            thread3.start();
            System.out.println("调用start方法，thread3当前状态：" + thread3.getState().toString());
            Thread.sleep(200L);
            System.out.println("等待200毫秒，线程遇到锁被堵塞时的状态：" + thread3.getState().toString());
        }
        Thread.sleep(3000L); // 再等待3秒，让thread3执行完毕，再看状态
        System.out.println("等待3秒，线程抢到锁并执行结束时的状态：" + thread3.getState().toString());
    }
}

程序运行结果显示：

• 当一个线程被创建时（还未调用start方法）处于NEW状态；
• 调用start方法后，线程开始执行，此时线程处于RUNNABLE状态；
• 当线程遇到锁被堵塞时线程进入BLOCKED状态
• 线程继续执行，一段时间后，线程正常执行结束，此时线程处于TERMINATED状态。
  ==（新建 -> 运行 -> 阻塞 -> 运行 -> 终止，NEW-> RUNNABLE->BLOCKED->RUNNABLE-> TERMINATED）==